The arms and the vent are 1 1/2" which is almost standard for a lavatory. IF the arms had to be longer, then a 2x1 1/2x2x2 fixture fitting might be used. Even with the "sweeps", good plumbing practice dictates that cleanout be installed in the vertical pipe, unless it is dropping directly into the main line. In the picture, IF I had to offset the fitting, I would have used 45's to make a "slight" jog and installed the fitting to the left closer to that sink than the right hand one.